Re: more power from my 4 cyl YJ automatic......how
Sosa...your asking the right questions....both Leve and Greg are right....Besides the cost of a header, you have to modify the exhaust pipes....headers do nothing for low and mid range and are high maintenance....except for the TBI, there is nothing you can really do....
Keep the tires small....larger tires have a direct effect on effective gearing, hence, going up 2 sizes can make it feel like your pulling a 10 ton trailer. If you do want larger tires, then regear, that will get your performance back where you want it.
Air Pressure - Keep proper air pressure in the tires and it will roll easier.
Reduce wind resisance....not much you can do about the shape....but if you start adding all those bolt on "make it look cool" goodies, you will only slow it down. Don't waste money or effort on the body lift...increases wind resistance and does not really do much for you.
With the price of gas....I think you are just fine right now with that 4 banger...tough engine....and it's fuel injected...low maintenace.